Raman scattering generally refers to the inelastic scattering of photons. When light scatters from an atom or molecule, a fraction of the photons induces a transition to or from an excited state of the atom or molecule, which produces scattered photons having a different frequency from the frequency of incident photons. The frequencies of the Raman scattered photons are characteristic of the atoms or molecules from which the photons scatter, which permits spectral analysis to identify chemical analytes. However, the fraction of photons scattered by Raman scattering is generally small, e.g., about 1 per 107 elastically scattered photons, and methods for enhancing the signal associated with Raman scattering have been developed. In particular, Surface Enhanced Raman Scattering (SERS) enhances the Raman scattering through interactions of scattered photons with rough metal surfaces or nanoparticles. Such enhancement is believed to result from resonances in localized surface plasmons interacting with photons and analytes. Methods and systems for further enhancing the Raman scattering signal and/or improving chemical analysis based on Raman scattering are sought.
Use of the same reference symbols in different figures indicates similar or identical items.